A COMPARATIVE-STUDY OF INTAKE AND DIGESTIBILITY OF FORAGES IN HERBIVORES - A REVIEW

Using literature data, we compared the ability of different domestic herbivores to ingest and digest forages. Sheep were used as reference animals. In sheep and goats on maintenance diets, dry matter intake (DMI) was similar, except for low quality roughages (eg, late hay and straw), of which DMI was higher in goats (+21%). After live-weight (LW) correction, DMI in bovines on maintenance diets was lower than in sheep, especially during long days (summer). During short days (winter) DMI in bovines was comparable to that in sheep. Nevertheless, the DMI expressed per kg LW0.75 was always higher in bovines. In the herbivore species above, DMI varies with age, breed and nutritional requirements. Sheep and deer ingested high quality forages at the same level, but deer appeared to ingest better low quality forages. The DMI per kg LW was similar for dromedaries and bovines, but with a tendency of being lower in dromedaries. Llamas seemed to have lower DMI than sheep. Finally, DMI per kg LW in horses was generally comparable with that in bovines. Unlike bovines, DMI in horses is unrelated to the forage cell-wall content. Cell-wall digestibility in goats in slightly higher (1.3 units) than in sheep. For low quality forages, however, this digestibility is markedly higher (+2.7 units) in goats, possibly due to a better selection of the ingested material. Organic matter (OM) digestibility, however, was similar in sheep and goats. The superiority of bovines over sheep to digest cell walls (+3 units) was clear. Thus, digestion of especially low quality roughage was more efficient in bovines than in sheep. Forage OM digestibility, except that of heather, was lower in deer (-3.5 units) than in sheep. In contrast, digestibility in camelids was higher (3-4 units). Finally, the digestibility of different forages in horses was markedly lower than in sheep (-2-3 units for legumes, -4 units for grass hays and -8 units for straw). In conclusion to this review, 2 important findings can be underlined: (i) the digestibility differences between herbivores are more evident for low quality forages with high cell-wall contents; and (ii) the total OM digestion is generally related to live-weight and nutritional requirements are proportional to LW0.75, and so herbivores can more easily adjust their requirements when their body weight is increased.